= Constants

Libraries of physical and chemical constants for scientific calculations in Ruby.

== Description

Constants provides libraries of constant values such as the precise mass of carbon 13, or the spin of a strange quark. When applicable, the constant values include uncertainty and units (via {ruby-units}[http://rubyforge.org/projects/ruby-units]). Also provides Constants::Library to index and generate common collections of constant values.

I have attempted to use reputable sources for the constants data (see below). Please notify me of any errors and send me suggestions for other constants to include.

• Rubyforge[http://rubyforge.org/projects/bioactive]
• Lighthouse[http://bahuvrihi.lighthouseapp.com/projects/13504-constants/overview]
• Github[http://github.com/bahuvrihi/constants/tree/master]

== Usage

require 'constants' include Constants::Libraries

Element predefines all chemical elements

c = Element::C c.name # => "Carbon" c.symbol # => "C" c.atomic_number # => 6 c.mass # => 12.0 c.mass(13) # => 13.0033548378

A smorgasbord of lookups methods

Element['Carbon'] # => Element::C Element['C'] # => Element::C Element[6] # => Element::C

=== Custom Libraries

Making a new constants library is straightforward using the Constants::Library module. The following example is adapted from the molecule[http://github.com/bahuvrihi/molecules/tree/master] library (a subproject of constants).

A library of amino acid residues.

class Residue attr_reader :letter, :abbr, :name

def initialize(letter, abbr, name)
  @letter = letter
  @abbr = abbr
  @name = name
end

A = Residue.new('A', "Ala", "Alanine")
C = Residue.new('C', "Cys", "Cysteine")
D = Residue.new('D', "Asp", "Aspartic Acid")
# ... normally you'd add the rest here ...

include Constants::Library

# add an index by an attribute or method
library.index_by_attribute :letter

# add an index where keys are calculated by a block
library.index_by 'upcase abbr' do |residue|
  residue.abbr.upcase
end

# add a collection (same basic idea, but using an array)
library.collect_attribute 'name'

end

index access through []

Residue['D'] # => Residue::D Residue['ALA'] # => Residue::A

access an index hash or collection array

Residue.index('upcase abbr') # => {'ALA' => Residue::A, 'CYS' => Residue::C, 'ASP' => Residue::D} Residue.collection('name') # => ["Alanine", "Cysteine", "Aspartic Acid"]

As you can see, Constants::Library allows the predefinition of common views generated for a set of constants. Nothing you couldn't do yourself, but very handy.

== Known Issues

• Particle data is from an unreliable source
• Constants::Constant could use some development; constants should support mathematical operations and comparisons based on uncertainty as well as value.
• Ruby doesn't track of the order of constant declaration until Ruby 1.9. Constants are indexed/collected as they appear in [module].constants

== Installation

Constants is available as a gem through RubyForge[http://rubyforge.org/projects/bioactive]. Use:

% gem install constants

== Info

Copyright (c) 2006-2008, Regents of the University of Colorado. Developer:: {Simon Chiang}[http://bahuvrihi.wordpress.com], {Biomolecular Structure Program}[http://biomol.uchsc.edu/], {Hansen Lab}[http://hsc-proteomics.uchsc.edu/hansenlab/] Support:: CU Denver School of Medicine Deans Academic Enrichment Fund Licence:: MIT-Style

=== Element Data

Element isotope, mass, and abundance information was obtained from the NIST {Atomic Weights and Isotopic Compositions}[http://www.physics.nist.gov/PhysRefData/Compositions/index.html] reference. All isotopes with a non-nil isotopic composition (ie relative abundance) were compiled from this {view}[http://www.physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=&all=all&ascii=ascii2&isotype=all] on 2008-01-22.

=== Physical Constant Data

The physical constant data is assembled from the NIST {Fundamental Physical Constants}[http://www.physics.nist.gov/cuu/Constants/Table/allascii.txt] on 2008-04-28.

Constants adds several units to ruby-units to support the physical constants reported in the NIST data. These are (as reported in the NIST data):

electron-volt:: 1.602176487e-19 joules kelvin:: 1.3806504e-23 joules hartree:: 4.35974394e-18 joules

=== Particle Data

Particle data was assembled from a non-ideal source, wikipedia[http://www.wikipedia.org/], and will remain so until I have time to update it with something better.